Exploring the causal relationship between body mass index and keratoconus: a Mendelian randomization study.

Background: Despite reports suggesting a link between obesity and keratoconus, the causal relationship is not fully understood. Methods: We used genome-wide association study (GWAS) data from public databases for a two-sample Mendelian randomization analysis to investigate the causal link between body mass index (BMI) and keratoconus. The primary method was inverse variance weighted (IVW), complemented by different analytical techniques and sensitivity analyses to ensure result robustness. A meta-analysis was also performed to bolster the findings' reliability. Results: Our study identified a significant causal relationship between BMI and keratoconus. Out of 20 Mendelian randomization (MR) analyses conducted, 9 showed heterogeneity or pleiotropy. Among the 11 analyses that met all three MR assumptions, 4 demonstrated a significant causal difference between BMI and keratoconus, while the remaining 7 showed a positive trend but were not statistically significant. Meta-analysis confirmed a significant causal relationship between BMI and keratoconus. Conclusion: There is a significant causal relationship between BMI and keratoconus, suggesting that obesity may be a risk factor for keratoconus.

Factors affecting meibomian gland area loss in symptomatic adults.

AIM: To characterize the distribution of meibomian gland (MG) area loss (MGL) and its relationship with demographic characteristics, mites, and symptoms. METHODS: This retrospective observational study included patients who visited the Dry Eye Clinic of Shenzhen Eye Hospital between June 2020 and August 2021. General patient characteristics, ocular symptoms, Demodex test results of the eyelid edges, and the results of a comprehensive ocular surface analysis were collected. MGL was analyzed using Image J software. RESULTS: This study enrolled 1204 outpatients aged 20-80 (40.70±13.44)y, including 357 males (29.65%) and 847 females (70.35%). The patients were classified into mild (n=155; 12.87%), moderate (n=795; 66.03%), severe (n=206; 17.11%), and extremely severe (n=48; 3.99%) MGL groups. MGL was significantly larger in female than in male (P=0.006). The degree of MGL also significantly differed in age (P<0.001) and the more numbers of mites with severity (P<0.001). Multivariate disordered multinomial logistic regression analysis identified that female sex, older age, secretory symptoms, and a large number of mites were risk factors for MGL (P<0.05). CONCLUSION: Patients with MGL are more likely to be older, female, more numbers of mites, and increased secretion.

Expression of ATP-Binding Cassette Transporter A1 (ABCA1) in Eyelid Tissues and Meibomian Gland Epithelial Cells.

Purpose: To validate the adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1) expression and distribution in human eyelid tissues and meibomian gland epithelial cells. Methods: Meibomian gland tissues from human eyelids were isolated by collagenase A digestion and cultured in defined keratinocyte serum-free medium (DKSFM). Infrared imaging was used to analyze the general morphology of meibomian glands. Hematoxylin and eosin (H&E) staining and Oil Red O staining were used to observe the morphological structure and lipid secretion in the human meibomian gland tissues. Quantitative real-time polymerase chain reaction, western blotting, and immunostaining were used to detect the mRNA and protein expression and cytolocalization of ABCA1 in the meibomian gland tissues and cultured cells. Results: The degree of loss of human meibomian gland tissue was related to age. Meibomian gland lipid metabolism was also associated with age. Additionally, human meibomian gland tissues express ABCA1 mRNA and protein; glandular epithelial cells express more ABCA1 mRNA and protein than acinar cells, and their expression in acinar cells decreases with differentiation. Furthermore, the expression of ABCA1 was downregulated in abnormal meibomian gland tissues. ABCA1 was mainly localized on the cell membrane in primary human meibomian gland epithelial cells (pHMGECs), whereas it was localized in the cytoplasm of immortalized human meibomian gland epithelial cells (iHMGECs). The mRNA and protein levels of ABCA1 in pHMGECs were higher than those in iHMGECs. Conclusions: Meibomian gland tissues of the human eyelid degenerate with age. ABCA1 expression in acinar cells decreases after differentiation and plays an important role in meibomian gland metabolism.